In the tropics, secondary forests are often “ephemeral,” succumbing to deforestation every 10 years or so and thus never able to fully recover

During a recent visit in Panama, a tour guide pulled our boat up alongside a stretch of clear-cut canal bank, muddy and exposed in the tropical sun. Developers needed that tract of jungle gone—at least for the time being. "Don't worry," the guide told us. "It'll grow back in a couple months. The jungle moves fast."

In a sense, he is right: nature is quick to sprout up seedlings and shrubs after a disturbance. That tract of jungle, however, likely will never be the same. According to new research conducted along the Panama canal by the Smithsonian Tropical Research Institute, even after enjoying 32 years in which to regrow, sections of formerly disturbed jungle never quite returned to its original glory of diversity. In fact, the researchers went to far as to label those regrown plots as relatively useless for biodiversity conservation.

The team randomly chose 45 regrown plots of forest throughout the Panama canal watershed and conducted surveys of all plant life there. The forests ranged in age from two to 32 years old. All in all, the team counted around 52,000 plants of 324 different species. Those patches that were located near still-intact old growth forests harbored higher species diversity than those that were more cut off from the original forest.

This sounds like a lot of trees are happily living in regrown patches, but the authors point out that those 324 species were not at all evenly distributed. Instead, the landscape was dominated by a few hardy pioneers. Just 7 percent of species popped up in more than half the plots, and still fewer of those species were frequently abundant.

When researchers also included trees in old growth forests, the species found in secondary forests represented just 55 percent of the total species diversity in the region. Worse still, even in the oldest plots surveyed, just half of the trees had reached reproductive maturity—they're not playing an active role yet in reseeding the jungle.

If given enough time, the authors think, secondary forests could likely regrow, mature and become productive, especially if they are located next to prevailing stretches of old growth. However, they point out, in the tropics secondary forests are often "ephemeral," succumbing to deforestation every 10 years or so and thus never able to fully recover.